#include <iostream>

using namespace std;

int main()
{
    int n;
    double a=1,b=2,c,sum=0;
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
        sum+=b/a;
        c=b;
        b=b+a;
        a=c;
    }
   printf("%.4lf",sum);
    return 0;
}
